Poster Presentation Society for Freshwater Science 2026 Annual Meeting

Spatial and temporal dynamics of benthic macroinvertebrates in the primary successional streams of Mount St. Helens (135187)

Shannon M Claeson 1 , Carri J LeRoy 2 , Deb S Finn 3
  1. U.S. Forest Service, PNW Research Station, Wenatchee, WA, USA
  2. The Evergreen State College, Olympia, WA, USA
  3. Missouri State University, Springfield, MO, USA

The eruption of Mount St. Helens (WA, USA) in 1980 obliterated forests and buried streams on the mountain’s north flank by over 100m of sterile pumice. Following the eruption, new spring-fed watersheds were created that flow into Spirit Lake. Community recovery was predicted to take many decades to centuries, but 36 years post-eruption we found significant benthic macroinvertebrate and algal community development (Claeson et al. 2021). Among six streams, large ranges in many physio-chemical characteristics existed, including water temperature, discharge, conductivity, organic carbon, nitrate, and riparian canopy cover. In 2016, hydrologic disturbance activity and cold-water temperatures (subsurface glacier source) appeared to limit successional development of aquatic communities. To better understand temporal diversity, benthic macroinvertebrates were collected from streams in July across three years (2019-2021) and every 3-weeks for one year (May-Nov. 2019). While inter- and intra-annual community variation was present within the streams, differences among streams were stronger. Community compositions were primarily driven by water temperature, discharge, and riparian canopy cover. The large differences in physical characteristics across the six streams provide a unique opportunity to explore in-stream community development and early stream succession.

  1. Shannon M. Claeson, Carri J. LeRoy, Debra S. Finn, Rosalina H. Stancheva, Emily R. Wolfe. 2021. Variation in riparian and stream assemblages across the primary succession landscape of Mount St. Helens, U.S.A. Freshwater Biology, 1-16. DOI: 10.1111/fwb.13694